Abstract
SUMMARY The taxonomic relationship between Gelidium elegans Kutzing and Gelidium subfastigiatum Okamura, two morphologically similar species of the red algal genus Gelidium (Gelidiaceae) growing in the north-western Pacific, was critically re-examined. Gelidium subfastigiatum has been distinguished from G. elegans by its more robust thalli, which have antrorse tooth-like branches, although their distinction has been said to be often difficult or impossible. We determined the nuclear encoded internal transcribed spacer 1 (ITS1) for 14 samples from eight populations of this G. elegans/ G. subfastigiatum complex, and two types of ITS1 sequences were found. Analysis of seasonal variations of subterminal portions of major branches revealed that this complex includes two groups: one possessing the type 1 ITS1 sequence and antrorse tooth-like branches that are subterminally thickened and widened during only colder months, and another possessing the type 2 ITS1 sequence and thin and narrow branches throughout the year. These groups should be recognized as separate species; the former is assigned to G. subfastigiatum and the latter to G. elegans.
Published Version
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